The horny layer of the skin covers the living body whereby retaining moisture and providing a defense against invasion by foreign substances. The horny layer is composed of various substances such as proteins including keratin and filaggrin, and lipids, produced by epidermal keratinocytes. Filaggrin fulfills the important role of forming a structure referred to as a keratin pattern by assembling keratin fibers into layers. Filaggrin is produced from profilaggrin, a precursor encoded by filaggrin gene (FLG), accompanying with keratinization, and causes agglomeration of keratin fibers. Moreover, filaggrin is decomposed in the upper corneal layer, thereby it is transformed into low molecular weight peptides and amino acids referred to as natural moisturizing factors, and is involved in moisture retention and absorption of ultraviolet rays.
In this manner, filaggrin is intimately involved in the moisture retention and barrier function of the horny layer of the skin, and a decrease in filaggrin production is involved in the onset of dry skin diseases such as ichthyosis vulgaris, atopic dermatitis or senile xerosis (Non-Patent Document 1). In order to maintain healthy and attractive skin condition, the suitable production of filaggrin and a suitable cycle of continuous cornification are required.
In consideration of the above, research has been conducted on substances that promote filaggrin synthesis, and plant extracts such as wild thyme extract, clove extract, salvia extract, etc., are already known to be substances having effects that promote filaggrin synthesis (Patent Document 1). In addition, ectoin, which is accumulated by certain species of bacteria in order to regulate osmotic pressure, is known to inhibit decreases in filaggrin caused by drying (Patent Document 2).